Vlad is playing on a swing set. His horizontal distance D(t) in m) from the center

Vlad is playing on a swing set.
His horizontal distance D(t) in m) from the center where being behind the center means a negative distance
as a function of time t (in seconds) can be modeled by a sinusoidal expression of the form a-cost-t) +
Att = 0, when he pushes off, he is 1 m behind the center, which is as far back as he goes. The shing reaches
the center - seconds later,